At least 97 people are missing and believed to have drowned after their Europe-bound boat sank in the Mediterranean Sea on Thursday, according to the Libyan coastguard.

Spokesman Ayoub Qassem said 23 migrants were rescued around 10 kilometres off the coast of Tripoli after authorities received a distress call. Fifteen women and five children are among those still missing.

Almost 230 refugees rescued off Libya's coast

The boat, which was packed with African nationals seeking asylum in Europe, "completely collapsed", he said.

The survivors, all men, were found clinging to a flotation device.

Those who had disappeared were "probably dead", Qassem said, adding that bad weather had prevented the recovery of their bodies.

Libya has become a key departure point for people risking their lives to cross the Mediterranean to Europe.

Hailing mainly from sub-Saharan countries, most of the asylum seekers board boats operated by people traffickers in the country's west, heading for the Italian island of Lampedusa 300 kilometres away.

Since the beginning of this year, at least 590 people have died or gone missing along the Libyan coast, the International Organisation for Migration said in late March.

In 2016, more than 5,000 people lost their lives at sea - an annual record - as they undertook perilous journeys to escape war, poverty, and persecution. In 2015, at least 3,771 refugees died while crossing the Mediterranean, up from 3,279 deaths the year before.

More than 24,000 asylum seekers arrived in Italy from Libya during the first three months of the year, up from 18,000 in the same period last year, according to the UN High Commissioner for Refugees.

The German government on Thursday said it would support a ban on the export of boats from the European Union to Libya as part of measures to stem the flow of people across the Mediterranean.

In February, EU leaders inked a deal to give $215mn to Libya's fragile government to stop migrant boats in the country's territorial waters.